Selenium cytotoxicity in Tetrahymena thermophila: New clues about its biological effects and cellular resistance mechanisms

Cellular Response of Adapted and Non-Adapted Tetrahymena thermophila Strains to Europium Eu(III) Compounds

Europium is one of the most reactive lanthanides and humans use it in many different applications, but we still know little about its potential toxicity and cellular response to its exposure. Two strains of the eukaryotic microorganism model Tetrahymena thermophila were adapted to high concentrations of two Eu(III) compounds (EuCl3 or Eu2O3) and compared to a control strain and cultures treated with both compounds. In this ciliate, EuCl3 is more toxic than Eu2O3. LC50 values show that this microorganism is more resistant to these Eu(III) compounds than other microorganisms. Oxidative stress originated mainly by Eu2O3 is minimized by overexpression of genes encoding important antioxidant enzymes. The overexpression of metallothionein genes under treatment with Eu(III) compounds supports the possibility that this lanthanide may interact with the -SH groups of the cysteine residues from metallothioneins and/or displace essential cations of these proteins during their homeostatic function. Both lipid metabolism (lipid droplets fusing with europium-containing vacuoles) and autophagy are involved in the cellular response to europium stress. Bioaccumulation, together with a possible biomineralization to europium phosphate, seems to be the main mechanism of Eu(III) detoxification in these cells.

Biogenic selenium nanoparticles and selenium/chitosan-Nanoconjugate biosynthesized by Streptomyces parvulus MAR4 with antimicrobial and anticancer potential

BACKGROUND

As antibiotics and chemotherapeutics are no longer as efficient as they once were, multidrug resistant (MDR) pathogens and cancer are presently considered as two of the most dangerous threats to human life. In this study, Selenium nanoparticles (SeNPs) biosynthesized by Streptomyces parvulus MAR4, nano-chitosan (NCh), and their nanoconjugate (Se/Ch-nanoconjugate) were suggested to be efficacious antimicrobial and anticancer agents.

RESULTS

SeNPs biosynthesized by Streptomyces parvulus MAR4 and NCh were successfully achieved and conjugated. The biosynthesized SeNPs were spherical with a mean diameter of 94.2 nm and high stability. Yet, Se/Ch-nanoconjugate was semispherical with a 74.9 nm mean diameter and much higher stability. The SeNPs, NCh, and Se/Ch-nanoconjugate showed significant antimicrobial activity against various microbial pathogens with strong inhibitory effect on their tested metabolic key enzymes [phosphoglucose isomerase (PGI), pyruvate dehydrogenase (PDH), glucose-6-phosphate dehydrogenase (G6PDH) and nitrate reductase (NR)]; Se/Ch-nanoconjugate was the most powerful agent. Furthermore, SeNPs revealed strong cytotoxicity against HepG2 (IC50 = 13.04 μg/ml) and moderate toxicity against Caki-1 (HTB-46) tumor cell lines (IC50 = 21.35 μg/ml) but low cytotoxicity against WI-38 normal cell line (IC50 = 85.69 μg/ml). Nevertheless, Se/Ch-nanoconjugate displayed substantial cytotoxicity against HepG2 and Caki-1 (HTB-46) with IC50 values of 11.82 and 7.83 μg/ml, respectively. Consequently, Se/Ch-nanoconjugate may be more easily absorbed by both tumor cell lines. However, it exhibited very low cytotoxicity on WI-38 with IC50 of 153.3 μg/ml. Therefore, Se/Ch-nanoconjugate presented the most anticancer activity.

CONCLUSION

The biosynthesized SeNPs and Se/Ch-nanoconjugate are convincingly recommended to be used in biomedical applications as versatile and potent antimicrobial and anticancer agents ensuring notable levels of biosafety, environmental compatibility, and efficacy.

In vitro evaluation of probiotic properties and selenium bioaccumulation of lactic acid bacteria isolated from poultry gastrointestinal, as an organic selenium source

The purpose of this study was to examine the probiotic characteristics and selenium (Se) bioaccumulation potential of five Lactobacillus strains in vitro. Lactobacillus acidophilus, L. delbrueckii subsp. lactis, L. reuteri, L. gallinarum, and L. animalis were among the strains employed. As significant aspects of probiotics, identification, and evaluation of their survival potential in the gastrointestinal system were undertaken. Although all experimental Lactobacillus strains bioaccumulated Se (IV) concentrations in media culture, three Lactobacillus strains (L. animalis, L. gallinarum, and L. acidophilus) bioaccumulated the highest Se concentrations (23.08, 8.62, and 8.51 mg/g, respectively) after culture in the presence of 1.5 mg/ml sodium selenite. By disc diffusion, all isolates were evaluated for antibiotic susceptibility against six antibiotics, including ciprofloxacin, ampicillin, methicillin, streptomycin, tetracycline, and trimethoprim-sulfamethoxazole. Many of the isolates tested positive for resistance to some of the antibiotics utilized. The L. reuteri and L. gallinarum were found to be resistant to about 50% of the antibiotics that were tested. In terms of acid tolerance, L. animalis showed significant resistance at acidic pH by 1.72 log unit reduction whereas L. delbrueckii and L. galliinarum showed significant sensitivity at acidic pH (P > 0.05). Bile tolerance was addressed as an important aspect of the safety assessment for probiotics. There were variances in acid and bile tolerance among species, although all of them tolerated stress conditions to an acceptable degree. Upon comparing the various species, it was observed that L. gallinarum exhibited a significant decline in growth, as evidenced by a decrease of 1.39 log units in cell viability. On the other hand, L. acidophilus and L. animalis demonstrated remarkable bile tolerance, with 0.09 and 0.23 log unit reduction respectively (P < 0.05). These results suggest that L. animalis, L. gallinarum, and L. acidophilus, can be good candidates to evaluate them in vivo in further investigations due to their tolerance to acid, and bile, antibiotic resistance, and strong ability to bioaccumulate Se in chickens.

Augmented dissemination of antibiotic resistance elicited by non-antibiotic factors

The emergence and rapid spread of antibiotic resistance seriously compromise the clinical efficacy of current antibiotic therapies, representing a serious public health threat worldwide. Generally, drug-susceptible bacteria can acquire antibiotic resistance through genetic mutation or gene transfer, among which horizontal gene transfer (HGT) plays a dominant role. It is widely acknowledged that the sub-inhibitory concentrations of antibiotics are the key drivers in promoting the transmission of antibiotic resistance. However, accumulating evidence in recent years has shown that in addition to antibiotics, non-antibiotics can also accelerate the horizontal transfer of antibiotic resistance genes (ARGs). Nevertheless, the roles and potential mechanisms of non-antibiotic factors in the transmission of ARGs remain largely underestimated. In this review, we depict the four pathways of HGT and their differences, including conjugation, transformation, transduction and vesiduction. We summarize non-antibiotic factors accounting for the enhanced horizontal transfer of ARGs and their underlying molecular mechanisms. Finally, we discuss the limitations and implications of current studies.

Selenite bioreduction by a consortium of halophilic/halotolerant bacteria and/or yeasts in saline media

Selenium oxyanions are released into environments by natural and anthropogenic activities and are present in agricultural and glass manufacturing wastewater in several locations worldwide. Excessive amounts of this metalloid have adverse effects on the health of living organisms. Halophilic and halotolerant microorganisms were selected for selenium oxyanions remediation due to presence of significant amount of salt in selenium-containing wastewater. Effects of aeration, carbon sources, competitive electron acceptors, and reductase inhibitors were investigated on SeO₃^2- bio-removal. Additionally, NO₃^--containing wastewater were exploited to investigate SeO₃^2- remediation in synthetic agricultural effluents. The results showed that the SeO₃^2- removal extent is maximum in aerobic conditions with succinate as a carbon source. SO₄^2- and PO₄^3- do not significantly interfere with SeO₃^2- reduction, while WO₄^2- and TeO₃^2- decrease the SeO₃^2- removal percentage (up to 35 and 37%, respectively). Furthermore, NO₃^- had an adverse effect on SeO₃^2- biotransformation by our consortia. All consortia reduced SeO₃^2- in synthetic agricultural wastewaters with a 45-53% removal within 120 h. This study suggests that consortia of halophilic/halotolerant bacteria and yeasts could be applied to treat SeO₃^2--contaminated drainage water. In addition, sulphates, and phosphates do not interfere with selenite bioreduction by these consortia, which makes them suitable candidates for the bioremediation of selenium-containing wastewater.

Intracellular bioaccumulation of the rare earth element Gadolinium in ciliate cells resulting in biogenic particle formation and excretion

Ciliates are abundant unicellular organisms capable of resisting high concentrations of metal ions in the environment caused by various anthropogenic activities. Understanding the cellular pathways involved in resistance to and detoxification of elements is required to predict the impact of ciliates on environmental element cycles. Here, we investigated the so far unknown process of tolerance, cellular uptake and bioaccumulation of the emerging rare earth element gadolinium (Gd) in the common ciliate Tetrahymena pyriformis. Gd treatment results in the intracellular formation and excretion of biogenic Gd-containing particles. This cellular process effectively removes dissolved Gd from the organic growth medium by 53.37% within 72 h. Based on light and electron microscopic observations, we postulate a detoxification pathway: Cells take up toxic Gd³⁺ ions from the medium by endocytosis, process them into stable Gd-containing particles within food vacuoles, and exocytose them. Stable biogenic particles can be isolated, which are relatively homogeneous and have a diameter of about 3 µm. They consist of the elements Gd, C, O, P, Na, Mg, K, and Ca. These findings broaden the view of metal ion accumulation by protists and are of relevance to understand environmental elemental cycles and may inspire approaches for metal recovery or bioremediation.

Stimuli-Responsive Silica Silanol Conjugates: Strategic Nanoarchitectonics in Targeted Drug Delivery

The design of novel drug delivery systems is exceptionally critical in disease treatments. Among the existing drug delivery systems, mesoporous silica nanoparticles (MSNs) have shown profuse promise owing to their structural stability, tunable morphologies/sizes, and ability to load different payload chemistry. Significantly, the presence of surface silanol groups enables functionalization with relevant drugs, imaging, and targeting agents, promoting their utility and popularity among researchers. Stimuli-responsive silanol conjugates have been developed as a novel, more effective way to conjugate, deliver, and release therapeutic drugs on demand and precisely to the selected location. Therefore, it is urgent to summarize the current understanding and the surface silanols' role in making MSN a versatile drug delivery platform. This review provides an analytical understanding of the surface silanols, chemistry, identification methods, and their property-performance correlation. The chemistry involved in converting surface silanols to a stimuli-responsive silica delivery system by endogenous/exogenous stimuli, including pH, redox potential, temperature, and hypoxia, is discussed in depth. Different chemistries for converting surface silanols to stimuli-responsive bonds are discussed in the context of drug delivery. The critical discussion is culminated by outlining the challenges in identifying silanols' role and overcoming the limitations in synthesizing stimuli-responsive mesoporous silica-based drug delivery systems.

Metabolic alteration of Tetrahymena thermophila exposed to CdSe/ZnS quantum dots to respond to oxidative stress and lipid damage

CdSe/ZnS Quantum dots (QDs) are possibly released to surface water due to their extensive application. Based on their high reactivity, even small amounts of toxicant QDs will disturb water microbes and pose a risk to aquatic ecology. Here, we evaluated CdSe/ZnS QDs toxicity to Tetrahymena thermophila (T. thermophila), a model organism of the aquatic environment, and performed metabolomics experiments. Before the omics experiment was conducted, QDs were found to induce inhibition of cell proliferation, and reactive oxygen species (ROS) production along with Propidium iodide labeled cell membrane damage indicated oxidative stress stimulation. In addition, mitochondrial ultrastructure alteration of T. thermophila was also confirmed by Transmission Electron Microscope results after 48 h of exposure to QDs. Further results of metabolomics detection showed that 0.1 μg/mL QDs could disturb cell physiological and metabolic metabolism characterized by 18 significant metabolite changes, of which twelve metabolites improved and three decreased significantly compared to the control. Kyoto Encyclopedia of Genes and Genomes analysis showed that these metabolites were involved in the ATP-binding cassette transporter and purine metabolism pathways, both of which respond to ROS-induced cell membrane damage. In addition, purine metabolism weakness might also reflect mitochondrial dysfunction associated with energy metabolism and transport abnormalities. This research provides deep insight into the potential risks of quantum dots in aquatic ecosystems.

Autophagy and lipid droplets are a defense mechanism against toxic copper oxide nanotubes in the eukaryotic microbial model Tetrahymena thermophila

The widespread use of inorganic nanomaterials of anthropogenic origin has significantly increased in the last decade, being now considered as emerging pollutants. This makes it necessary to carry out studies to further understand their toxicity and interactions with cells. In the present work we analyzed the toxicity of CuO nanotubes (CuONT) in the ciliate Tetrahymena thermophila, a eukaryotic unicellular model with animal biology. CuONT exposure rapidly induced ROS generation in the cell leading to oxidative stress and upregulation of genes encoding antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), metal-chelating metallothioneins and cytochrome P450 monooxygenases. Comet assays and overexpression of genes involved in DNA repair confirmed oxidative DNA damage in CuONT-treated cells. Remarkably, both electron and fluorescent microscopy revealed numerous lipid droplets and autophagosomes containing CuONT aggregates and damaged mitochondria, indicating activation of macroautophagy, which was further confirmed by a dramatic upregulation of ATG (AuTophaGy related) genes. Treatment with autophagy inhibitors significantly increased CuONT toxicity, evidencing the protective role of autophagy towards CuONT-induced damage. Moreover, increased formation of lipid droplets appears as an additional mechanism of CuONT detoxification. Based on these results, we present a hypothetical scenario summarizing how T. thermophila responds to CuONT toxicity. This study corroborates the use of this ciliate as an excellent eukaryotic microbial model for analyzing the cellular response to stress caused by toxic metal nanoparticles.

Arsenate and arsenite differential toxicity in Tetrahymena thermophila

A comparative analysis of toxicities of both arsenic forms (arsenite and arsenate) in the model eukaryotic microorganism Tetrahymena thermophila (ciliate protozoa) has shown the presence of various detoxification mechanisms and cellular effects comparable to those of animal cells under arsenic stress. In the wild type strain SB1969 arsenate is almost 2.5 times more toxic than arsenite. According to the concentration addition model used in binary metallic mixtures their toxicities show an additive effect. Using fluorescent assays and flow cytometry, it has been detected that As(V) generates elevated levels of ROS/RNS compared to As(III). Both produce the same levels of superoxide anion, but As(V) also causes greater increases in hydrogen peroxide and peroxynitrite. The mitochondrial membrane potential is affected by both As(V) and As(III), and electron microscopy has also revealed that mitochondria are the main target of both arsenic ionic forms. Fusion/fission and swelling mitochondrial and mitophagy, together with macroautophagy, vacuolization and mucocyst extruction are mainly associated to As(V) toxicity, while As(III) induces an extensive lipid metabolism dysfunction (adipotropic effect). Quantitative RT-PCR analysis of some genes encoding antioxidant proteins or enzymes has shown that glutathione and thioredoxin metabolisms are involved in the response to arsenic stress. Likewise, the function of metallothioneins seems to be crucial in arsenic detoxification processes, after using both metallothionein knockout and knockdown strains and cells overexpressing metallothionein genes from this ciliate. The analysis of the differential toxicity of As(III) and As(V) shown in this study provides cytological and molecular tools to be used as biomarkers for each of the two arsenic ionic forms.

Interactions between soil protists and pollutants: An unsolved puzzle

Soil protists are essential but often overlooked in soils, although they play crucial functional roles in the terrestrial ecosystem. While soil protists have drawn increased attention to their functional role in soils, their interaction with soil pollutants remains unresolved. This review provides a first overview of the current understanding of interactions between soil protists and major pollutants (heavy metals, organic pollutants, nanoparticles, and soil pathogens). We summarize how soil pollutants affect protists and vice versa, showing that we are just beginning to understand their complex interactions. In addition, we identify five research gaps, including hidden diversity, adaptive mechanisms, species interactions, soil bioindicators and environmental applications, and we hope that our review will help promote and build research guidelines for the future. In conclusion, a better understanding of soil pollutant-protist interactions will significantly increase our knowledge of the pollution ecology in the soil and how soil organisms respond and adapt to environmental pollution, which will contribute to the bioremediation and environmental applications of protists in soil.

Is selenium beneficial or detrimental to earthworm? Growth and metabolism responses of Eisenia Fetida to Na2SeO3 exposure

Se unevenly distributed in soils due to variations of geology and anthropogenic input, which results in different effects on earthworms. The effects of Se were characterized by analyzing the growth and metabolism responses of earthworms after exposure to three different concentrations of Na₂SeO₃. The results showed that except the possible growth promotion at 5 mg/kg, low and middle-level exposure to Na₂SeO₃ (0.3-10 mg/kg) did not significantly affect the growth of earthworms. While a significant inhibition effect on growth was observed in the high-level exposure group (30-70 mg/kg). There was an inflection point for Se performing promotion to inhibition effects on earthworm growth. To investigate the metabolic response of earthworms, a novel HPLC-ESI-MS (High Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry) method was used to determine sensitive biomarkers. Selenium exposure significantly altered the metabolism of seven essential amino acids, namely tyrosine, leucine, phenylalanine, valine, alanine, glycine, and lysine, and two selenoamino acids, namely selenomethionine and methylselenocysteine. The overall metabolism level of earthworms was not affected at low exposure concentrations, but was affected at medium and high exposure concentrations. The metabolic pathways that integrated the selenocompound metabolism and the tricarboxylic acid cycle from the perspective of energy supply and demand were affected by Na₂SeO₃ exposure. The derived reactive oxygen species at high exposure concentrations were probably the reason for the growth inhibition effect of Se on earthworms. This study provides biochemical insights into the effects of Na₂SeO₃ on earthworms and suggests that an Se concentration of about 2.3 mg/kg is appropriate for soil organism health.

Biomedical Applications of Mycosynthesized Selenium Nanoparticles Using Penicillium expansum ATTC 36200

In this study, green and eco-friendly biosynthesis of selenium nanoparticles (Se-NPs) were performed using Penicillium expansum ATTC 36200 for multiple biomedical applications. Mycosynthesized Se-NPs were completely characterized using UV, FT-IR, XRD, SEM, and TEM techniques. Se-NPs biosynthesized by P. expansum was characterized as a spherical shape with average size 4 to 12.7 nm. Moreover, Se-NPs were evaluated for multiple biomedical applications as antimicrobial, antioxidant, and anticancer activities and hemocompatibility. Results illustrated that Se-NPs have potential antimicrobial activity against Gram-positive (Bacillus subtilis ATCC6051 and Staphylococcus aureus ATCC23235), Gram-negative bacteria (Escherichia coli ATCC8739and Pseudomonas aeruginosa ATCC9027), fungi (Candida albicans ATCC90028, Aspergillus niger RCMB 02724 and Aspergillus fumigatus RCMB 02568), and antioxidant activity. Additionally, Se-NPs exhibited anticancer activity against PC3 cell line; IC50 was 99.25 μg/mL. Meanwhile, they showed non-hemolytic activity on human RBCs at concentration up to 250 μg/mL. In conclusion, biosynthetic Se-NPs by P. expansum are promising for many safe-use biomedical applications.

Identification of glutathione-S-transferase m19 and m34 among responsive GST genes against 1-chloro-2,4-dinitrobenzene treatment of Tetrahymena thermophila

Industrial xenobiotic pollutants have toxic effects on diverse organisms in their natural environments. This study aims to identify the Glutathione-S-transferases (GST) from Tetrahymena thermophila that are highly responsive to the treatment of synthetic substrate 1-chloro-2,4-dinitrobenzene (CDNB). The LD50 value of CDNB was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test as 0.079 mM at 9 h exposure. The glutathione affinity-purified 22 kDa and 23 kDa GSTs from CDNB-treated cells were identified as GSTm19 and GSTm34 with 2D-gel electrophoresis coupled MALDI-Tof MS/MS analysis. The specific activitiy of the affinity-purified GSTs was upregulated upon the treatment of 0.072 mM CDNB with the decreased cell survival. GSTm19 and GSTm34 had also upregulated the mRNA expression under the highest dose treatment. The high cell survival and elevated total GST enzyme activity at 9 h under CDNB doses could be the result of both transcriptional upregulations as well as post-translational modifications. As a result, the cell survival of Tetrahymena thermophila was significantly affected by CDNB exposure in a concentration-dependent manner with the effect of low-dose stimulation and high-dose inhibition.

Effect of Selenium Nanoparticles on Germination of Hordéum Vulgáre Barley Seeds

Within the framework of this study, the effect of nanoparticles of the essential trace element selenium stabilized by Polyvinylpirrolidone (PVP) C15 (8 ± 2 kDa) and ascorbic acid on the germination of barley seeds has been studied. Selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid, characterized by a spherical shape, monodisperse size distribution, and a diameter of about 70 ± 5 nm, were obtained by the chemical reduction method. The experiment compared the effect of selenium nanoparticles and selenous acid on seed germination. The positive effect of preparation of selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid on the length of roots and shoots, the number of roots, and the percentage of seed germination has been revealed. It was determined that the highest percentage of Hordeum vulgare L. culture seed germination was achieved using a preparation of selenium nanoparticles stabilized by PVP C15 (8 ± 2 kDa) and ascorbic acid at a concentration of of 4.65 µg/mL. Analysis of the results showed that selenium in the form of nanoparticles has an order of magnitude that is less toxic than in the form of selenous acid. The study of morphological and functional parameters during the germination of Hordeum vulgare L. seeds allowed us to conclude that selenium nanoparticles can be successfully used in agronomy and agriculture to provide plants with the essential microelement selenium, which is necessary for the normal growth and development of crops.

Detoxification of ionic liquids using glutathione, cysteine, and NADH: Toxicity evaluation by Tetrahymena pyriformis

Ionic liquids (ILs), also known as green solvents, are widely acknowledged in several fields, such as chemical separation, synthesis, and electrochemistry, owing to their excellent physiochemical properties. However, their poor biodegradability may lead to environmental and health risks, posing a severe threat to humans, thus requiring further research. In this study, the biotoxicities of the imidazolium-based ILs were evaluated in Tetrahymena pyriformis. Moreover, IL detoxification was investigated by addition of glutathione (GSH), cysteine, and nicotinamide adenine dinucleotide (NADH). Reactive oxygen species (ROS) initiated by different IL types caused damage to Tetrahymena, while glutathione, cysteine, and NADH eliminated ROS, achieving the detoxification purposes. Detoxification results showed that NADH exhibited the best detoxification ability, followed by glutathione and cysteine. Finally, RT-PCR results suggested that metallothionein might have participated in IL detoxification.

Will a Non-antibiotic Metalloid Enhance the Spread of Antibiotic Resistance Genes: The Selenate Story

The rapid emergence of antibiotic resistance genes (ARGs) has become an increasingly serious threat to public health. Previous studies illustrate the antibiotic-like effect of many substances. However, whether and how commonly used or existing non-antibiotic metalloids (e.g., selenate) would enhance ARG spread remains poorly known. Here, we tracked the long-term operation of a bioreactor continuously fed with selenate for more than 1000 days. Metagenomic sequencing identified 191 different ARGs, of which the total abundance increased significantly after the amendment of selenate. Network analyses showed that ARGs resisting multiple drugs had very similar co-occurrence patterns, implying a potentially larger health risk. Host classification not only indicated multidrug-resistant species but also distinguished the mechanism of ARG enrichment for vertical transfer and horizontal gene transfer. Genome reconstruction of an ARG host suggested that selenate and its bioreduction product selenite could stimulate the overproduction of intracellular reactive oxygen species, which was confirmed by the direct measurement. Bacterial membrane permeability, type IV pilus formation, and DNA repair and recombination were also enhanced, together facilitating the horizontal acquirement of ARGs. Overall, this study for the first time highlights the ARG emergence and dissemination induced by a non-antibiotic metalloid and identifies ARG as a factor to consider in selenate bioremediation.

Biofortification of soybean (Glycine max L.) with Se and Zn, and enhancing its physiological functions by spiking these elements to soil during flowering phase

Soybean is recognized as one of the most important prospective protein sources for human nutrition under conditions of climate change and population growth. Occurrence of Se and Zn deficiency in vast areas over the globe inhabited by up to 2 billion people, induced search for a comprehensive solution to these problems through the efficient Se/Zn biofortification of soybean seeds (beans). To assess the Se/Zn accumulation efficiency and the physiological status of soybean plants, a pot experiment on Se and Zn enrichment in beans was conducted. It consisted of applying 15 different Se-deficient soil treatments with these elements during the flowering phase, alone or in dose combinations. Application of Se alone, besides Se accumulation in soybean, reduced Zn uptake from soil, but caused alterations in Zn translocation, and its multiple enrichment in beans. Addition of Zn alone promoted both Zn and Se enrichment in beans. Joint Se/Zn application in increasing doses appeared to have a strong synergistic effect on accumulation of these elements in beans and enhanced the physiological functions of the soybean. This manifested itself in the growth of photosynthetic production and soybean biomass, and in the improvement of lipid peroxidation status (REC, MDA and proline content indices). Toxicity symptoms indicated the maximum Se/Zn doses. Several-fold higher contents of Se and Zn in soybean straw compared to spiked soil suggest its possible use as Se/Zn-rich soil amendment in accordance with the circular economy goals. These novel findings may significantly contribute to human health improvement in Se and Zn deficient regions.

Salicylic acid antagonizes selenium phytotoxicity in rice: selenium homeostasis, oxidative stress metabolism and methylglyoxal detoxification

We investigated the mechanistic consequences of selenium (Se)-toxicity, and its possible mitigation using salicylic acid (SA) in rice. In comparison with control, sodium selenate-exposed 'Se1' (0.5 mM) and 'Se2' (1.0 mM) plants showed accumulation of Se by 190.63 and 288.00 % in roots, 2359.42 and 2054.35 % in leaf sheaths, and 7869.91 and 9063.72 % in leaves, respectively, resulting in severe toxicity symptoms, such as growth inhibition, chlorosis, burning of leaves, and oxidative stress. In contrast, SA addition to Se-stressed plants significantly alleviated the Se-toxicity symptoms, and radically improved shoot height (28.88 %), dry biomass (34.00 %), total chlorophyll (37.51 %), soluble sugar (17.31 %) and leaf water contents (22.31 %) in 'SA + Se2' plants over 'Se2' plants. Notably, SA maintained Se-homeostasis, and decreased 'Se2'-induced oxidative stress by enhancing ascorbate level (67.75 %) and the activities of antioxidant enzymes like superoxide dismutase (20.99 %), catalase (40.97 %), glutathione peroxidase (12.26 %), and glutathione reductase (32.58 %) relative to that in 'Se2' plants. Additionally, SA protected rice plants from the deleterious effects of methylglyoxal by stimulating the activities of glyoxalase enzymes. Furthermore, SA upregulated several genes associated with reactive oxygen species (e.g. OsCuZnSOD1, OsCATB, OsGPX1 and OsAPX2) and methylglyoxal (e.g. OsGLYI-1) detoxifications. These findings unravel a decisive role of SA in alleviating Se-phytotoxicity in rice.

Exposure to a high selenium environment in Punjab, India: Biomarkers and health conditions

Seleniferous areas have been identified and described in many parts of the world. Despite the interest in selenium as a trace element of considerable toxicologic and nutritional relevance, however, only a few studies have been carried out on human health effects of such high selenium environments. We collected blood, hair and nail samples from 680 adult volunteers (267 men and 413 women) living in seven villages located in the seleniferous area of Punjab, India. We measured selenium levels in these specimens. We also administered a questionnaire to collect information about diet and other lifestyle characteristics, to identify the sources of selenium exposure and to correlate it with a number of health conditions. Serum and hair selenium contents were highly correlated, while the association of these biomarkers with nail selenium content was weaker. Serum selenium showed limited association with consumption of locally produced foods, while pulses and vegetables, along with cereals and pulses, were associated to higher hair and nail selenium contents, respectively. Association of a number of adverse health endpoints with serum and hair selenium was stronger than for nail selenium contents. Such endpoints included higher prevalence of nausea and vomiting, bad breath, worm infestation, breathlessness exert and bad breath, chest pain, hair and nail abnormalities and loss, garlic odor, edema, spontaneous abortion, and overall selenosis. In contrast, we gathered no evidence of dermatitis or loss of appetite in residents most exposed to selenium. Overall, and despite some statistical imprecision in effect estimates, these results confirm the occurrence of adverse health effects in subjects exposed to high levels of environmental selenium. Nail selenium contents may be less adequate to reflect and monitor such overexposure, compared with blood and hair levels.

Exposure to a high selenium environment in Punjab, India: Effects on blood chemistry

Many studies have shown that overexposure to environmental selenium may exert a wide pattern of adverse effects on human health, but much uncertainty still surrounds some of them as well as the exact amounts of exposure involved. In particular, very few studies have addressed the possible changes in blood chemistry following high selenium exposure. In a Northeastern part of Punjab, India, very high soil selenium content has been documented, with a value exceeding 2 mg/kg (up to 5) as compared with the <0.5 mg/kg selenium content characterizing the surrounding referent areas. In seven villages located in that seleniferous areas, we carried out a survey by recruiting volunteers and sampling blood, hair and nail specimens. We administered a questionnaire to the participants and analyzed the specimens for the selenium, along with a series of biochemical and haematological parameters in blood. We included 680 adult volunteers (267 men and 413 women), who showed median selenium levels of 171.30 µg/L in serum, 1.25 µg/g in hair, and 5.7 µg/g in nails. Overall, increasing selenium exposure tended to correlate with higher levels of total cholesterol, albumin, free triiodothyronine, deionidase activity, and with red cell and platelet counts. After stratifying the subjects according to category of selenium exposure, we observed a dose-response relation between serum selenium and risk of high total cholesterol, and between hair selenium and risk of high total and low-density lipoprotein cholesterol, high pancreatic lipase, altered thyroid-stimulating hormone and free triiodothyronine levels. Nail selenium exposure category positively correlated with risk of high alanine-aminotransferase, altered albumin levels, high pancreatic lipase and low levels of thyroid-stimulating hormone. Chronic selenium overexposure appears to adversely affect lipid profiles and pancreatic, liver, and thyroid function, with selenium biomarkers having different abilities to predict such effects.